Field of the Invention
The invention relates to a two-part or multipart housing for sensors, especially pressure and flow sensors, with a bottom part as the process connection and a top part as the component receiver which therefore contains most or all of the electrical and electronic components.
Sensors which are used to monitor a medium or the property of a medium, for example, the pressure of a liquid or a gas, consist generally of at least two parts, the bottom part being connected to a container or pipe which carries the medium, and therefore often also being called the process connection. These sensors are mainly pressure or flow sensors, but can also, for example, be capacitive fill level sensors. In these sensors, the housing is used, on the one hand, like all sensors, to protect the sensor and the associated electronics, but on the other, also for reliable and permanent connection to the medium-carrying pipe or container.
The advantage of a sensor with a two-part or multipart housing is that, when there is a defect of the sensor or electronics, only the upper part of the housing, need be replaced without the need to intervene in the running process by replacing the process connection. But in these housings, one problem is the connection between the bottom part which is used as the process connection and the top part which contains the bulk of the electronics and which often has a plug or cable connection for this purpose.
In the known housing of the initially mentioned type, the process connection consists of nickel-plated brass. It is produced by turning from standardized hexagonal solid material, part of the original hexagonal surface being maintained as a key surface. For connection to the measurement medium it has an inside or an outside thread. The bottom part of the housing is connected to the top part by a press fit, knurling being formed on the top end of the bottom part. The wall thickness of the top part which is made as a pipe section, for cost reasons generally as a welded pipe section, decreases gradually in the direction to the knurling.
The disadvantage in this known housing is that by pressing the top part onto the bottom part the protective nickel layer is partially damaged in the area of the knurling and the underlying brass is not very resistant chemically. This is especially disadvantageous when the measurement medium is chemically corrosive. Another major disadvantage is that with regard to the inside diameter of the top part and the outside diameter of the bottom part in the area of the press fit only very small tolerances are allowable. The forces to be expended for the press fit and the loading capacity of the connection depend largely on these tolerances. Since the wall thickness of the top of the press fit is very low, cracks or deformations of the top part can occur.
Housings of the above described type are also known in which the top part and the bottom part of the housing are welded or screwed to one another. If the top part and the bottom part are welded together, of course the electronics can no longer be replaced without intervening in the process. Since the electrical connection, which is often a plug-and-socket connection, is very short between the top part and the bottom part, due to improper screwing and overly large tolerances of the threads a displacement of the top part relative to the bottom part can occur which can no longer ensure reliable operation of the sensor.